1. Field of the Invention
The present invention relates to an electrostatic discharge (ESD) protection device. More specifically, the present invention relates to an ESD protection device with both positive voltage and negative voltage tolerance.
2. Description of Related Art
ESD damage is usually caused by direct electrostatic discharge from a charged conductor to an electrostatic discharge sensitive device (ESDS), electrostatic discharge from the ESDS or by field-induced discharges. ESD simulation models include the human-body model (HBM), the machine model (MM), and the charge-device model (CDM). Electronic components and circuits, which are not provided with suitable protection, are highly susceptible to ESD damage.
Since the electronic products are required to be miniaturized and light-weighted, the sizes of the components in the integrated circuitry need to shrink. Accordingly, the IC designers have to consider ESD protection capability of the internal circuit and adjust the design of the internal circuit, in order to prevent the devices on the IC from being damaged by ESD voltage. Since ESD voltage is much larger than the power supply voltage, ESD voltage will damage adjacent semiconductor devices when the ESD phenomenon occurs. Hence, it is very important to prevent ESD voltage from entering into the internal circuit. In order to prevent ESD voltage from entering the internal circuit of an IC and causing damage, adequate ESD protection is required for the IC.
The input/output (I/O) terminals in most ICs operate either using only positive (or high) voltage signals, or only negative voltage signals. Hence, traditional ESD protection devices provide ESD protection for the I/O terminals of a single working voltage level (either positive or negative voltage). However, as electronic products become multifunctional, the IC needs to output or input positive and negative voltage signals in one connecting terminal. For example, a source driver IC of a LCD panel is required to output positive or negative voltage signals in one connecting terminal (the channel for driving the LCD panel). For the traditional ESD protection devices, it is impossible to offer ESD protection for positive and negative voltages by a single ESD protection device. Hence an improved ESD protection device having positive voltage as well as negative voltage tolerance is required to enable devices to withstand positive as well as negative ESD voltages at the same time.